Haemophilus influenzae
Cultural characteristics
Biochemical characters
Phylum Proteobacteria, Class Gammaproteobacteria, Order Pasteurellales, Family Pasteurellaceae, Genus Haemophilus,
Haemophilus influenzae (Lehmann and Neumann 1896) Winslow, Broadhurst, Buchanan, Krumwiede, Rogers and Smith 1917, with
six serovars (a-f, based on the structure of capsular polysaccharides) and seven biovars (I-VII, based on three biochemical
characteristics: indole production, urease and ornithine decarboxylase activities).
Haemophilus influenzae biovar VIII were shown to
be distinct from
H. influenzae and were assigned to the not validly published taxon “H. intermedius subsp. gazogenes”.
Burbach (1987) proposed two subspecies, designated “
H. influenzae subsp. influenzae” (includes strains of serovars a,c, and f, all
belonging to biovars II,III, and VII; ornithine decarboxylase negative) and “
H. influenzae subsp.meningitidis” (includes strains of
serovars a,b,d and e; biovars I,II,IV, and V are represented among these strains; ornithine decarboxylase positive, excepting a single
biovar II strains ).
Historical synonyms:
Influenzabacillus Pfeiffer 1892, Bacterium influenzae Lehmann and Neumann 1896, Mycobacterium
influenzae  (Lehmann and Neumann)
Chester 1901, Coccobacillus pfeifferi Neveu-Lemaire 1921, Haemophilus meningitidis
(Martins) Hauduroy et al. 1937.
Gram negative, 0.3-0.5 / 0.5-3.0 µm ,rods or coccobacilli, nonmotile,  but fresh clinical
isolates express peritrichous pili with hemagglutinating properties which are lost after
subcultivations. Fimbrial structures have been demonstrated in otitis media isolates
of noncapsular strains. Many strains produce capsules.
Colonies on chocolate agar are smooth, low, convex, grayish, translucent, 0.5-1.0 mm
in diameter in 24 h. and 1-1.5 mm in 48h. Capsulated strains produce larger and more
mucoid colonies  (1-3 mm) with tendency to coalesce.
On transparent agar media , colonies of capsulated strains show iridescence when
examined under obliquely transmitted light.
Morphologically atypical strains produce more granular colonies.
Hemolysis is negative. Aerobic, facultatively anaerobic, require X-factor and V-factor for
growth. CO
2 is not required. Optimum temperature 35-37 ºC. Growth on Mac Conkey
agar is negative.  
Obligate parasites and form part of the mucous membranes of the human upper respiratory tract; found exclusively behind the
palatinal arches; is present in the nasopharynx of a majority of healthy children. The carriage rate in adults is lower.
Has not been detected in any animal species apart from cimpanzees.
Serovars b and f are most frequently encountered, whereas serovar c is rare.
Capsules play a part in pathogenesis, determination of type specificity, and induction
of anti-infective immunity. Outer membrane proteins (P1, P2, P4, P5, P6) are important
as a means of typing and as potential vaccine candidates.
Fresh clinical isolates express peritrichous pili with hemagglutinating properties which
are lost after subcultivations. Fimbrial structures have been demonstrated in otitis
media isolates of non-capsular strains.
Possesses neuraminidase activity.
Produce an extracellular endopeptidase (IgA1 protease) capable of inducing specific
cleavage of  a proline-serine or a proline-threonine peptide bond in the hinge region
of human immunoglobulin A1.
Endotoxin have a small role in patogenesis. No exotoxin produced.
It is involved in:
a] acute , pyogenic and usually invasive infections in which
H. influenzae (almost
exclusively encapsulated strains of  serovar b) is the primary pathogen (meningitis in
children, epiglottitis, cellulitis, arthritis, osteomyelitis, septicemia, pneumonia)
b] non-invasive infections (often chronic) in which primarily non-capsulated H. influenzae play an important, though in many cases
probably a secondary part (chronic bronchitis, sinusitis, conjunctivitis, otitis media, and lower respiratory disease in children)
Occasionally are isolated from genital, pelvic, and urinary tract infections.

Experimental infection was successfully reproduced on monkey (bronchopneumonia & meningitis), mouse (deadly peritonitis), young
rat (bacteremia & deadly meningitis in 1-2 hours after serovar b intranasal inoculation), Guinea pig and rabbit (deadly toxemia in 1-2
  1. Mogens Kilian, 2004.Genus III. Haemophilus . In:  Bergey’s Manual of Systematic Bacteriology, Second edition,Vol two, part B,
    George M. Garrity (Editor-in-Chief),   pp. 883-904.
  2. Mary P.E. Slack, 2006.Haemophilus. In: Topley & Wilson’s Microbiology and Microbial Infections, 10 edition, Vol. 2, Bacteriology,
    Edward Arnold Ltd.
  3. Pozsgi N., 1985. Genul Pasteurella. In: Bacteriologie medicala, vol II, v. Bilbiie, N. Pozsgi (sub redactia), Ed. Medicala, Bucuresti,
  4. N. Mihancea si colab., 2009.Identificarea genului Haemophilus. In: Tratat de microbiologie clinica, D. Buiuc, M. Negut, Ed.
    Medicala, Bucuresti, 797-809.
  5. J. G.Holt et al., 1994.Begey’s manual of Determinative Bacteriology, 9th-edition, Williams & Wilkins.
Nitrates reduction, oxidase, alkaline phosphatase, catalase, acid from D(+) glucose, D(+) xylose, D(+) galactose & maltose are

2S, arginine dehydrolase, glycerol, xylitol, L(+) arabinose, dulcitol, meso-inositol, mannitol, D(-) sorbitol, D(-) fructose, D(+)
mannose, L(+) rhamnose, L(-) sorbose, cellobiose, lactose, ONPG, D(+) melibiose, sucrose (saccharose), trehalose, raffinose,
inulin, salicin, α-glucosidase (PNPG) & gas from D(+) glucose are negative.

(1), lysine decarboxylase, ornithine decarboxylase (2) & indole (3) are variable.

(1) urease test is positive for biovars I,II,III,IV and negative for biovars V,VI,VII.
(2) ornithine decarboxylase is positive for biovars I, IV, V (
H. influenzae subsp. meningitidis) & VI and negative for biovars II,III,VII (H.
influenzae subsp. influenzae
(3) indole test is positive for biovars I,II,V,VII and negative for biovars III,IV,VI.
(c) Costin Stoica
Culture media
Biochemical tests
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